1. Field of the Invention
The invention is a blood reservoir with at least one pliable wall having at least three innovative features. First, the compliant reservoir is sealed within a rigid housing allowing control of the xe2x80x9catmosphericxe2x80x9d pressure surrounding the bag, and therefore the pressure at which the bag would collapse. This first invention enables vacuum augmented venous drainage (VAVD) with a collapsible soft-shell reservoir (i.e. venous bag) and is particularly useful for cardiopulmonary bypass. Second, the invention incorporates means that improve gas bubble removal from blood transiting the collapsible reservoir. Third, a reservoir with all ports extending from its top is disclosed, an innovation that provides easy loading/unloading of the reservoir in/out of its holder and simplifies sealing the reservoir in a chamber thereby allowing the aforementioned VAVD.
2. Description of the Prior Art
Blood is routinely pumped outside the body during dialysis, cardiopulmonary bypass, and long-term cardiac and/or respiratory support (e.g. extracorporeal membrane oxygenation, ECMO). In general, blood flows from the venous side of the patient to a venous reservoir that is usually maintained at atmospheric pressure. Blood flow from the patient to the reservoir is a function of the resistance of the fluid conduit between patient and reservoir, and the pressure difference between patient and reservoir. When the reservoir is maintained at atmospheric pressure, that pressure difference is the height difference between patient and reservoir; the resulting flow is referred to as gravity drainage. Venous drainage by gravity alone provides inadequate return during procedures such as minimally invasive cardiac surgery and bypass via femoral cannulation. Usually it is the resistance of the venous cannula that limits the flow rate. Vacuum augmented venous drainage (VAVD) is a technique that overcomes flow limitations by applying suction to the hard shell reservoir thereby increasing the pressure difference between the venous cannulation site and venous reservoir. VAVD allows for a decrease in the inner diameter of the venous line, thereby reducing prime volume and enabling the 1o use of a smaller cannula, which translates to an easier insertion, a better surgical view and a smaller surgical incision. This method precludes the use of the safer soft-shell closed venous reservoir (venous bag) unless a more expensive and complicated two-pump system is used (see McKusker K, Hoffman D, Maldarelli W, Toplitz S, and Sisto D. High-flow femoro-femoral bypass utilizing small cannulae and a centrifugal pump on the venous side, see Perfusion 1992; 7:295-300.
Clinically, a venus bag is used because it provides significant safety features. If the ba emptiels, it collapses, thereby preventing gross air from being pumped to the patient. It usually has no air-blood interface, and it requires no antifoam agents that can embolize into the blood. A recent study by Schonberger et al (Schonberger JPAM, Everts PAM, and Hoffmann J J. xe2x80x9cSystemic blood activation with open and closed venous reservoirs. Annals of Thoracic Surgery, 1995; Vol. 59, pages 1549-55) comparing the hard shell to the bag reservoir found significantly lower blood activation, shed blood loss, crystalloid infusion, and hemolysis, and less donor blood infusion with the bag reservoir. Schonberger""s group recommended against routine use of an open (hard shell) venous reservoir system. Currently, a slight negative pressure applied to the venous line (to facilitate blood drainage) using a single pump is possible with less desirable hard shell venous reservoirs. It is impossible to apply negative pressure to current soft-shell reservoirs, but it is possible with the present invention.
In an open, hard shell reservoir, air escapes by floating to the top of the reservoir. In a bag reservoir, air floats to the top but must be actively eliminated. This can be done manually with a syringe, or more frequently with a roller pump operating slowly so as to continuously pump fluid to the cardiotomy reservoir. With either method, a sudden large volume of air can overwhelm the air removal system and cause disastrous consequences, especially without a vigilant perfusionist. With one preferred embodiment of the present invention, air would be eliminated automatically without a roller pump or intervention by the perfusionist, and priming of the extracorporeal circuit would be facilitated through faster air removal utilizing either a floating ball valve or a hydrophobic membrane. Currently there are devices used in the CPB circuit that incorporate hydrophobic membranes that remove air yet do not allow blood to cross (e.g. Model # AutoVent-SV, Pall Corp Glen Cove N.Y.). Studies with filters used in these applications have shown that the membranes clear air from water almost indefinitely (many days), even if high suction is applied, without reducing gas transfer rate over time. However, when the membrane is exposed to blood, especially when high suction is applied, a film forms on the membrane over time, causing a significant increase in resistance to gas flow. The present invention incorporates designs and means to reduce this problem and extend the life of the membrane when used with blood. Likewise, U.S. Pat. No. 3,849,071 shows a floating ball within a blood filter that supposed to open a purge port when air enters and close when the blood level rises. However, as described, it is a physical impossibility for the ball to xe2x80x9cfallxe2x80x9d and open the purge port because, as shown, the weight of the floating ball is insufficient to overcome the force holding the ball against the purge port. With the present invention, the relative weight of the ball, the internal diameter of the purge port, and the suction applied to the purge port are designed to assure that the ball will drop to open the purge port in response to air level in the venous reservoir.
With prior art soft-shell reservoirs (SSR) air may be trapped at the top of the liquid by the collapsed walls of the reservoir, see FIGS. 1a and 1aa. U.S. Pat. No. 4,622,032 illustrates a soft shell reservoir having an inlet tube extending from the bottom half way into the reservoir. This arrangement helps bubbles move up to the top of the extended tubes but the bubbles can still be trapped above said tubes. U.S. Pat. No. 5,573,526 illustrates the prior art soft-shell reservoir having its gas removal tubes (i.e. 18 and 20 of FIG. 1) extending from the top less 40% of the height of its blood chamber into the reservoir. All other prior art SSR have air removal tubes that are shorter with many having vent tubes that do not extend into the SSR at all (e.g. U.S. Pat. No. 5,580,349). As FIGS. 1b and 1bb illustrate, a tube extending from the top and into the SSR prevents complete collapse of the pliable walls of the bag thereby forming a pathway for air to move upward. The prior SSR air removal tubes extend less than 40% of the height of the blood chamber and therefore air still may be trapped below said tubes.
A soft shell venous reservoir sold by [Johnson and Johnson (and now by]Medtronic, Model # Maxima 1386[see Reference 13)]shows a soft shell reservoir with an inline tube extending, along one side of, along one side of the bag, to the gas purge port at a 45xc2x0 incline. This design has a rigid fluid path between blood inlet and gas purge port. However, this design is not as conducive to air removal as a vertical fluid path would be. In addition, the tube extending between inlet tube and purge port had an ID of ⅝xe2x80x3, or only 25% greater diameter than the inlet tube. Thus, the velocity of the liquid in the column slows to only 64% of the inlet velocity. In another aspect of the present invention, a vertical path is provided from the blood inlet at the bottom of the bag to the gas purge port at the top of the bag, such path limiting the aforementioned problem of trapped air. The vertical path also has a large enough diameter that slows the velocity of the liquid to 25% or less of the inlet velocity. A lower blood velocity is more conducive to bubble removal.
State of the art soft shell venous reservoirs with a screen are designed such that a large portion of the screen contacts the internal walls of the bag, thereby increasing the resistance to blood flow across the screen, and rendering that portion of the screen ineffective, at least partially.
This contact between the screen and the walls of the bag increases as the volume in the reservoir decreases. One aspect of the present invention reduces that problem by preventing the external walls of the venous reservoir from contacting the screen.
The indication of blood level in present soft shell venous reservoir is very inaccurate and low level, or air-in-the-reservoir, alarms are not reliable because many are designed for hard shell reservoirs. The present invention provides effective means to alarm at low blood levels and in the soft shell venous reservoir.
Currently, at the end of the bypass procedure, the patient is weaned off the heart lung machine by reducing the bypass flow. This is achieved by partially clamping the venous line and decreasing the speed of the arterial pump. Once off bypass, the blood left in the venous reservoir is gradually pumped back to the venous side of the patient. Another aspect of the invention allows the user to adjust the positive pressure applied to the blood within the venous reservoir. By being able to increase the pressure of the venous reservoir, the user can effectively reduce venous drainage or perfuse the blood back to the patient. This is not possible with current venous reservoir bags and may be dangerous with hard shell reservoirs (i.e., air may be pushed to the patient).
The inventor has also previously described an inline bladder (The Better-Bladder(trademark), now U.S. Pat. No. 6,039,078), a device with a thin walled, sausage shaped bladder sealed inside a clear, rigid housing. Since the bladder is made from a single piece of tubing, the blood path is smooth with no flow discontinuities. The bladder portion is sealed within the housing that has an access port to the housing space outside the bladder. Because of its thin wall, the enlarged section can easily collapse. Thus, it can serve as an inline reservoir, providing compliance in the venous line to reduce the pressure pulsations at the pump inlet. The Better-Bladder also transmits the blood pressure flowing through it across its thin wall, allowing pump inlet pressure to be measured noninvasively by measuring the gas pressure of the housing via the gas port. The degree of xe2x80x9cgravity drainagexe2x80x9d is user-adjustable by setting the negative pressure in the Better-Bladder housing. If the suction generated by the venous pump becomes too great, the pump is slowed or stopped by a pump controller. The Better-Bladder does not have a gas purge port or a screen to inhibit gas bubbles. It is also much smaller, having nominal volume of 80 ml for adult perfusion lo as compared to over 1,000 ml for a venous reservoir.
Despite users acknowledgement that SSR are safer, hard shell reservoirs are easier to use and therefore more widely used. For example, it is easier to connect the inlet tubing located at the top of the hard shell reservoir than to the inlet tube of the SSR located at the bottom. Though some SSRs are premounted by the manufacture to a supporting plate (e.g. Cobe see U.S. Pat. No. 5,693,039), most require multiple hanging hooks for proper support (e.g. Baxter""s SSR model # BMR1900 has 3 holes at the top and 4 holes at the bottom), an inconvenience at best, a danger in an emergency. Present mounted SSR do not improve the tube connection by much. It would be a clinical advantage to provide a SSR that allows fast mounting and dismounting, and tube connection that are easy or even easier than that of hard shell reservoir. Another requirement for present SSR is the use of a supporting faceplate (e.g. see FIG. 3 of U.S. Pat. No. 5,573,526). These are used to improve the bubble path from the blood to the top of the reservoir. Such faceplates are again inconvenient, require additional assembly time by the user, and may obstruct the direct approach to the front wall of the bag. The latter isuseful when bubbles xe2x80x9cstuckxe2x80x9d on the wall are to be dislodged. The elimination, or at least the reduced requirement, of a front plate is another desirable attribute.
U.S. Pat. No. 5,823,045 xe2x80x9cMeasuring Blood Volume in Soft-Shell Venous Resevoirs (sp.) by Displacementxe2x80x9d illustrates a SSR enclosed in a rigid housing. This invention suggests sealing a SSR within a rigid housing but does not suggest applying vacuum to the fluid surrounding the SSR. In fact, neither the FIGS. nor the specifications mention a port for adjusting the fluid in sealed container 12. Van Driel""s patent has some major flaws. The tubes connected to the bag are to be xe2x80x9cthreaded through resilient seals 26 in the bottom of container 12 . . . xe2x80x9d also renders ""045 clinically irrelevant. If, though not described as such, container 12 is disposable, then the system as described is too expensive. If, as understood, container 12 were not disposable, then xe2x80x9cthreadingxe2x80x9d the tubes would break sterility, and would be very difficult, especially if a seal is required. Further, since the outside diameter of perfusion connectors are larger than the OD of the tubing they connect, it would be impossible to have any of the tubing of the SSR connected to anything until after they have been threaded. In addition, the housing needs to be sufficiently wide for the user to place their hands and thread the inlet and outlet tubes at the bottom of box 12, a major disadvantage that hinders quick setup and increases the likelihood of contamination. This invention has not been reduced to clinical practice.
Since the SSR is sealed in container 12, external means are provided by ""045 to xe2x80x9cmassagexe2x80x9d the SSR with xe2x80x9cvibratorxe2x80x9d 36. In fact, since vibrator 36 is not connected to the wall of the SSR, it can only squeeze the wall rather than the pull and push motions required for vibration. This provides significantly less manipulation ability as compared to direct contact with the bag.
PCT""s International Publication Number WO 99/08734 entitled xe2x80x9cSystem and Method for Minimally Invasive Surgery Vacuum-Assisted Venous Drainagexe2x80x9d illustrates in FIG. 9a standard SSR (xe2x80x9cpreferably BMR-800 or BMR-1900xe2x80x9d) completely sealed in a rigid housing. It is also suggested that xe2x80x9c. . . a pressure differential between the interior and exterior of the reservoir . . . xe2x80x9d be maintained. This design is as impractical as that of U.S. Pat. No. ""045. If the bag and rigid housing are assembled and shipped to the end user as a single unit, the unit becomes very expensive and therefore would be used only for VADV cases. The expense arises from a housing required to support a large force. The force can be calculated as (Pressure)*(Area). Thus, to support a pressure of xe2x88x92250 mmHg with a safety factor of 2 for a box that holds a bag like the BMR-1900 (10xe2x80x3 high by 12xe2x80x3 wide), the force on each faceplate is 1200 lb! The inventors did not suggest, nor showed or described, a mechanism for the user to seal the bag in the box. Even if there was a mechanism, it would be very difficult, time consuming, and, as described with relation to ""045, most likely to break sterility. And, once sealed it would be impossible for the user to contact the bag.
Both ""045 and ""08734 illustrate the rigid housing as a rectangular box. A better design to support the large external force due to the large area and vacuum used would be an ellipsoid cross section or at least rounded comers.
Both ""045 and ""08734 illustrate the great need for designs that allow simple, inexpensive, and quick means to seal and remove the bag from its container even with long tubing or large connectors without affecting its sterility. Simple and quick means to reach the enclosed bag would also be welcomed. The present invention overcomes these clinically non-workable prior art designs.
It is standard practice to place the venous reservoir above the oxygenator to assure that the microporous membrane is always under positive pressure. A negative pressure would result in air crossing the membrane and entering the arterial line, a very dangerous situation. When VAVD is used, suction can be applied to the venous reservoir only once the arterial pump is generating a positive pressure in the arterial line. Otherwise, the suction applied to the venous reservoir can draw air across the membrane. A one-way valve at the pump outlet prevents vacuum applied to the venous reservoir from reaching the membrane oxygenator, but a one-way valve incorporated into the outlet of the present venous reservoir is preferable. Means to assure that the gas side of the membrane oxygenator is always positive relative to the blood side would also be a major safety feature for all VAVD applications.
The present invention incorporates improved designs for venous reservoirs that provide the benefits of prior art devices (limiting pump suction using the safer, pliable blood reservoir) while avoiding their disadvantages (air entrapment, inability to utilize VAVD, required vigilance for air removal). Further, its advantages and uniqueness are also enhanced by providing the user with means to adjust the degree of suction applied for venous augmentation and assuring that a greater area of the screen is effective in liquid transport.
Briefly, the present invention in its simplest form consists of a blood reservoir having at least one pliable wall, a blood inlet, a blood outlet, and a gas purge port. In one preferred to embodiment, a first structure having tubular cross section and semirigid wall is placed above said inlet thereby providing a first path for undesirable bubbles entering the reservoir to move to the top where they are eliminated via said gas purge port. The first structure preferably has an effective cross section that is larger than the ID of said inlet tube thereby slowing any blood flow and allowing more favorable conditions (longer time, lower drag) for gas bubbles to float upward. The wall of the first structure is sufficiently rigid to prevent collapse of said pliable wall from blocking said first path. In another preferred embodiment, the pliable wall of the venous reservoir is sealed externally, forming a pressure chamber external to the venous reservoir. Controlled suction applied to said external chamber is transmitted across said pliable wall thereby controlling the negative pressure of the blood at which said pliable wall moves.
Another preferred embodiment has all the tubes at the top of the SSR. These tubes pass through, sealed within, and physically supported by a rigid disposable supporting plate providing three major advantages. First, the bag is supported by hanging the supporting plate in a supporting fixture, much like the hard shell reservoir. This allows the user to xe2x80x9cdrop inxe2x80x9d the SSR and just as easily remove the SSR from its holder. Second, the supporting plate provides simple sealing means along a single plane, an extremely important feature for simple and secure sealing of the SSR within housing for VAVD applications. Third, by having all the tubes for the bag entering from its top, the bottom of the bag is unhindered and can be placed lower to the floor allowing greater gravity drainage. In addition, because the bag hangs from the top, the weight of the SSR/blood contributes to the seal of the supporting plate against the housing. Designed properly, this gravitational force can eliminate or greatly simplify any clamping required by other designs.
It is therefore the objective of the present invention to provide an improved venous blood reservoir with at least one pliable wall that provides a path for gas bubbles entering the inlet to move unhindered up to the gas purge port.
A further objective of the present invention is an improved venous blood reservoir, having at least one pliable wall, allowing the user to adjust the negative pressure applied to said pliable wall thereby allowing for augmented venous drainage.
A further objective of the present invention is an improved venous blood reservoir designed to maintain its external wall from contacting the screen material and thereby reducing the resistance to blood flow across the screen.
Yet another objective of the present invention is to incorporate a one-way valve at the outlet of the venous reservoir, said valve preventing blood from being sucked into the venous reservoir when pressure at the outlet of the venous reservoir is positive relative to the liquid pressure in the venous reservoir.
Another objective of the present invention is to provide an improved venous blood reservoir with at least one pliable wall that when placed at the pump inlet, provides compliance that reduces pressure fluctuations at said pump inlet.
Another objective of the present invention is to provide an improved venous blood reservoir with at least one pliable wall that when placed at the pump inlet, provides automated means to eliminate air.
Another objective of the present invention is to provide an improved venous blood reservoir with at least one pliable wall and with a relatively large gas purge port, said port providing a more volumetrically effective gas purge, and one that is less traumatic to the blood.
Another objective of the present invention is to provide automated means to detect air in the venous reservoir and utilize said means to alarm the user or control the suction used to remove air from the venous reservoir.
Another objective of the present invention is to provide the user with a SSR that is simple to use, and easy to load and unload from its holder or from its container.
Another objective of the present invention is to provide the user with a SSR having all its connections above the bag facilitating said connections and allowing a lower placement of the reservoir thus providing greater gravity drainage.
Another objective of the present invention is to utilize gravity to facilitate sealing of the SSR in its VAVD container.
Another objective of the present invention is to utilize the applied suction to facilitate sealing the SSR within its VAVD container.
Another objective of the present invention is to provide a single plane to seal SSR in VAVD container.
Another objective of the present invention is to provide a non-disposable VAVD container that supports at least xe2x88x921000 mmHg.
Another objective of the present invention is to provide a disposable cover/holder as part of the SSR for the VAVD container.
Yet another objective of the present invention is to provide a single venous bag that can be used with either standard or with VAVD thus, reducing cost of inventory and simplifying the user""s set up.
Another objective of the present invention is to provide a disposable SSR incorporating a structure that facilitates sealing the bag within a non-disposable VAVD container, thus reducing cost.
Another objective of the present invention is to provide a SSR incorporating means to prevent the SSR from pulling out of, or twisting within its holder.
Another objective of the present invention is to provide a means to allow suction application to both SSR and cardiotomy independent of the height difference between the two.
Another objective of the present invention is to provide a means to reduce the chance of gas pulled across the microporous membrane when suction is applied to the venous reservoir.
Another objective of the present invention is to provide a VAVD housing having an ellipsoid cross section that can better support a large external force and streamlined to the shape of the SSR.
Another objective of the present invention is to provide a VAVD housing for SSR that does not require the user""s hands to be placed within said housing when mounting said SSR in said housing
Other objectives, features and advantages of the present invention will become apparent by reference to the following detailed description, but nonetheless illustrative, of the presently preferred, embodiments thereof with reference to the accompanying drawings therein.